1. Field of the Invention
The present invention relates to an electro-mechanical energy converter and a vibration wave driving apparatus.
2. Description of the Related Art
In general, a vibration wave driving apparatus such as an ultrasonic motor (vibration wave motor) includes a vibrator which generates driving vibration as a basic configuration. The vibrator moves a contact body, which is pressurized by the vibrator, by using the driving vibration. The vibration wave driving apparatus has been used for camera lens driving, and conventional systems can take the form of an annular-type and a rod-type vibration wave driving apparatuses.
An example of the vibrator, which constitutes the basic configuration of the vibration wave driving apparatus, is illustrated in FIG. 10. A vibrator 900 includes a shaft e1, the bottom end of which is threaded, and a first elastic body a1 which is externally fitted on the shaft e1, is made of metal, and cylindrical with a small diameter. Further, the vibrator 900 includes a disk-shaped elastic body d1 which is externally fitted on the shaft e1 to come into contact with the first elastic body a1, and an electro-mechanical energy converter c1 which is externally fitted on the shaft e1 to come into contact with the disk-shaped elastic body d1. Further, the vibrator 900 includes a flexible substrate 11 which is externally fitted on the shaft e1 to come into contact with the electro-mechanical energy converter c1 in order to supply electricity to the electro-mechanical energy converter c1. Further, the vibrator 900 includes a metal-made, large diameter and disk-shaped second elastic body b1 which is connected with thread to the bottom end of the shaft e1, and sandwiches and fixes the disk-shaped elastic body d1, the electro-mechanical energy converter c1 and the flexible substrate 11. (for example, refer to Japanese Patent Application Laid-Open No. 2003-47266)
The electro-mechanical energy converter is not limited to the shape shown in FIG. 10. For example, as shown in FIGS. 11A and 11B, a cylindrical piezoelectric element laminated with a disk shaped piezoelectric element 1000 can be employed. In this laminated-piezoelectric element, first, a plurality of sheets made of a piezoelectric material which forms an electrode on the surface thereof are laminated to form a plate type board having a multi-layer structure, and this board is divided into a plurality of square lumps. Thereafter, the external shape of the divided square lumps is processed to form a disk shape. Thus the laminated-piezoelectric element is manufactured. On the surface of this piezoelectric element 1000, divided electrode films of a quadrant-shape 1001-1, 1001-2, 1002-1 and 1002-2 are formed split into four parts by a non-electrode part (electrode film boundary part) (FIG. 11A) Then, on the back of the piezoelectric element 1000, electrode film 1004 is formed (FIG. 11B) in its entirety. The divided electrode films 1001-1 and 1002-1 are charged with a plus voltage, and the divided electrode films 1001-2 and 1002-2 are charged with a minus voltage (for example, refer to U.S. Pat. No. 3,416,233).
There is a request for miniaturization of the vibration wave driving apparatus which uses the piezoelectric element laminated with the above-described disk shaped piezoelectric element 1000. If the piezoelectric element 1000 is simply made small with its disk shape intact, the area of an electrode film of the piezoelectric element 1000 becomes small and the output of the vibration wave driving apparatus becomes low.
Theoretically, the amplitude of the output of the vibration wave driving apparatus depends on a conversion rate from the displacement in a thickness direction of the piezoelectric element to the displacement of bending vibration of the vibrator. Since the conversion rate of a polygonal piezoelectric element is higher than the disk shaped piezoelectric element 1000 (FIGS. 11A and 11B), the output of the vibration wave driving apparatus using the polygonal piezoelectric element becomes higher than that using the disk shaped piezoelectric element 1000 (FIGS. 11A and 11B).
Therefore, an attempt has been made to change a form of the piezoelectric element 1000 from a disk shape to a polygon such as a square, thereby implementing the vibration wave driving apparatus which produces a high output. A two-phase AC signal having a phase difference of 90 degrees with each other is applied to the electro-mechanical energy converter c1 having driving phases which are out of phase with each other by 90 degrees. Thus, a progressive traveling wave is induced on the disk-shaped elastic body d1. The vibration wave driving apparatus utilizes frictional force produced by bonding with pressure to the disk-shaped elastic body d1 having abrasion resistance. Thus, the vibration wave driving apparatus drives a contact body using the traveling wave on the disk-shaped elastic body d1 (for example, refer to Japanese Patent Application Laid-Open No. 2003-47266).
However, with respect to a small vibration wave driving apparatus using the above-described polygonal piezoelectric element, the optimization of the shape of the divided electrode film has not been considered. Accordingly, if the divided electrode film is ingeniously shaped, the output can be further improved.